The BSA Machine Carbine was a series of submachine guns of British origin intended to replace the British Army's STEN gun. They were fed from a side-inserted folding box magazine and had an unusual cocking "sleeve" that functioned in a pump-action fashion.

This weapon was designed by Birmingham Small Arms in the mid-40's. It was first unveiled in 1945, where it was demonstrated at RSAF Enfield. It fired at 530 rounds per minute and performed impressively, despite being slightly heavy.

It was not until 1947 that trials for the weapon were arranged. It competed against the MCEM3 in June, and was deemed favourable over the MCEM3 due to its stability. The design was modified later that year and it was given a curved 30-round magazine and two alternative methods of cocking. This improved model once again trialed against the MCEM3 and several other contenders; the Australian Kokoda No.1 submachine gun, the Patchett gun, and the STEN gun. The trials were held at Pendine, starting on the 8th of September and ending on the 16th.

The BSA Machine Carbine got the best report of all the competitors and an order of 100 models was placed for troop trials. The costs of production proved so high that the order was reduced to a mere 6 models. The 6 weapons were tested and returned to BSA for improvements for the trigger mechanism, and adding bayonet fittings was now mandatory since GS specifications now required every submachine gun to be able to fit a bayonet. This proved inconvenient, since the unique cocking sleeve of the BSA Machine Carbine could not accept a bayonet. The whole cocking sleeve had to be redesigned. These modifications proved to be detrimental to the design, and in 1951 the weapon was tested against two different models of the Patchett gun, where it was discovered that the new redesigned cocking sleeve of the BSA Machine Carbine was fragile, stiff and awkward to strip.

In May 1951, the BSA Machine-Carbine was trialed against the Patchett gun, the Australian MCEM1, and the Madsen Model 50. The BSA Machine Carbine's cocking sleeve was still stiff and would not function in sandy conditions. It was decided that even if modified, the BSA Machine Carbine would be no better than the Patchett gun, and in 1952 the BSA Machine Carbine was rejected outright. BSA felt that the sudden changes of specifications had negatively impacted their design and was the reason for the weapon's failure.

The BSA Machine Carbine was a unique submachine gun design that incorporated an odd cocking mechanism. The fore-end was comprised of a plastic "sleeve" which was pumped forwards in order to cock the weapon. Initial models had straight magazines that were inserted into the side of the weapon, much like the STEN. The magazine well could fold back so the magazine did not stick out, but this was only to ease carrying and the weapon could not be fired in this configuration. It also had a folding wire stock. The large fire selector was on the left side of the pistol grip.